Freeform optics offer great flexibility in design parameters, but the subaperture techniques required for manufacture often result in mid-spatial frequency (MSF) errors that can impact final performance. These errors must be removed, but the options to do so, often requiring hand-smoothing by a skilled artisan, are costly and time-consuming. Optimax has developed the HERMES (High End Robotic MSF Elimination System) a robotic platform that uses a machine learning algorithm to smooth parts. Preliminary research indicated promising results, but the process had not yet been compared to the “gold standard” of human smoothing. Results indicate that HERMES fared well compared to smoothing results of a highly skilled artisan. Future directions for work are discussed.
There is a potential need for large (<500 mm diameter) conformal windows for use on air, space, and water craft. These windows need to fit the curvature of the vehicle, which results in extreme freeform geometries. “Extreme Freeforms” are a class of shapes that do not have rotational symmetry, must be polished using sub-aperture techniques, and whose deviation from a best-fit sphere is on the same order as the size of the part. This paper will discuss some of the challenges associated with manufacturing optics of this size and shape and how Optimax solved them. These challenges include: blank acquisition, a lack of viable commercially available polishing platforms for extreme freeform shapes, and metrology. A demonstrator optic was designed and manufactured from fused quartz. Final metrology data for both sides of the window will be shown and discussed.
With optical technology and design advances, larger freeform optics are increasingly sought after by consumers for an expanding number of applications. Many techniques have been developed to meet the challenges of producing these nonrotationally symmetric optics, which cannot be fabricated via traditional manufacturing and metrology processes. In the past, methods were established to create smaller freeforms. With demands for more and larger freeforms, manufacturers must scale up existing processes. This paper will present some of the challenges and solutions of extending freeform polishing capabilities from approximately 150 mm diameter parts to a component of over 500 mm in diameter. In fabricating the 500 mm freeform, Optimax has addressed many of the manufacturing and metrology challenges using some proprietary techniques as well as some novel methods. Some of the approaches explored in this paper include acquisition of a substrate blank of sufficient dimensions, material handling logistics, polishing strategies, and metrology. Earlier freeform polishing projects at Optimax utilized a smaller pick-and-place style, 6-axis robotic arm. The route to design, build, and program a scaled-up polishing robotic arm is discussed. Considerations for polishing path planning and metrology are explained. In addition, deflectometry, a non-interferometric measurement method using fringe reflection and ray tracing, has been developed in parallel to help measure mid-spatial frequency error on a part surface faster and more safely than traditional methods, as it can be done in-situ.
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